Effects of anxiety induced by conditioned fear on the expression of NMDA receptors and synaptic plasticity in the rat BLA

NMDA receptors (NMDAR) are vital in CNS activities such as anxiety, memory, and cognition, and the neurobiological mechanisms behind anxiety disorders are exceedingly complicated. The "glutamic acid theory" posits that glutamate excitotoxicity is a key pathophysiological mechanism in anxiety disorders. However, the exact mechanism by which conditioned fear contributes to anxiety disorders remains unknown.Based on the conditioned fear-induced anxiety disorder model, this work aims to investigate changes in NMDAR and related proteins throughout the acquisition and expression of fear memory, as well as the impact on synaptic structural and functional plasticity. Injecting the NMDA receptor endogenous agonist D-Serine (50 μg/μL) and the noncompetitive antagonist MK-801 (1 μg/μL) into the lateral ventricle of the conditioned fear model rats, as well as conducting behavioral observations, show that NMDAR are closely involved in the development of conditioned fear-induced anxiety. Model rats showed significant changes in glutamate (Glu) and γ-aminobutyric acid (GABA) levels in the amygdala (BLA), as well as expression of NMDAR and downstream BDNF/TrkB signaling pathway components. At the same time, model rats exhibited synaptic and neuronal injury, aberrant long-term potentiation (LTP), and decreased expression of essential synaptic proteins SYP and PSD-95. In conclusion, our study demonstrates that NMDAR and synaptic plasticity play a critical role in the development of conditioned fear-induced anxiety, serving as an important reference for understanding the neurobiological underpinnings of anxiety disorders and providing insights into their treatment and new possible targets.